Membranous nephropathy (MEM-bruh-nus nuh-FROP-uh-thee) occurs when the small blood vessels in the kidney (glomeruli), which filter wastes from the blood, become inflamed and thickened. As a result, proteins leak from the damaged blood vessels into the urine (proteinuria). For many, loss of these proteins eventually causes signs and symptoms known as nephrotic syndrome.

In mild cases, membranous nephropathy may get better on its own, without any treatment. As protein leakage increases, so does the risk of long-term kidney damage. In many, the disease ultimately leads to kidney failure. There's no absolute cure for membranous nephropathy, but successful treatment can lead to remission of proteinuria and a good long-term outlook.

Membranous nephropathy usually develops gradually, so you may not suspect that anything is wrong. As you lose protein from your blood, swelling in your legs and ankles and weight gain from excess fluid can occur. Some people experience lots of swelling from the very beginning of the disease, and others may not have any severe symptoms until they have advanced kidney disease.

Signs and symptoms of membranous nephropathy include:

Swelling in the legs and ankles

Weight gain

Fatigue

Poor appetite

Frothy urine

Elevated fat levels in the blood (hyperlipidemia)

Increased protein levels in the urine (proteinuria)

Decreased protein levels in the blood, particularly of the protein albumin

When to see a doctor

If you have blood in your urine, persistent swelling in your legs and ankles, or increased blood pressure, make an appointment to see a doctor.

In a majority of cases of membranous nephropathy, evidence of autoimmune activity can be found. Your body's immune system mistakes some of your own tissues as foreign and attacks them with autoantibodies. These autoantibodies can damage your kidney's filtering systems (glomeruli).

Sometimes membranous nephropathy is brought on by other causes, notably:

Autoimmune disease, such as lupus erythematosus

Infection with hepatitis B, hepatitis C or syphilis

Certain medications, such as gold salts and nonsteroidal anti-inflammatory drugs

Solid cancerous tumors or blood cancers

Membranous nephropathy may also occur along with other kidney diseases, such as diabetic nephropathy and rapidly progressive (crescentic) glomerulonephritis.

Factors that can increase your risk of membranous nephropathy include:

Having a medical condition that can damage your kidneys. Certain diseases and conditions increase your risk of developing membranous nephropathy, such as lupus and other autoimmune diseases.

Use of certain medications. Examples of medications that can cause membranous nephropathy include nonsteroidal anti-inflammatory drugs and gold salts.

Exposure to certain infections. Examples of infections that increase the risk of membranous nephropathy include hepatitis B, hepatitis C and syphilis.

High cholesterol. Levels of cholesterol and triglycerides are often high in people with membranous nephropathy, which greatly increases the risk of heart disease.

Blood clots. With proteinuria, you may lose proteins that help prevent clotting from your blood into your urine. This makes you more prone to having blood clots develop in deep veins or blood clots that travel to your lungs.

Infections. You're more susceptible to infections when proteinuria causes you to lose immune system proteins (antibodies) that protect you from infection.

Nephrotic syndrome. High protein levels in the urine, low protein levels in the blood, high blood cholesterol, and swelling (edema) of the eyelids, feet and abdomen can lead to nephrotic syndrome — a cluster of signs and symptoms that affect your kidneys' filtering ability.

Acute kidney failure. In cases of severe damage to the kidneys' filtering units (glomeruli), waste products may build up quickly in your blood. You may need emergency dialysis to remove extra fluids and waste from your blood.

Chronic kidney disease. Your kidneys may gradually lose function over time to the point where you need dialysis or a kidney transplant.

You'll likely start by seeing your primary care doctor if you have signs or symptoms of kidney disease. If lab tests reveal you have kidney damage, you may be referred to a doctor who specializes in kidney problems (nephrologist).

What you can do

To get ready for your appointment, ask if there's anything you need to do ahead of time, such as limit your diet. Ask a friend or family member along to your appointment to help you remember important points later. Then make a list of:

Your symptoms, including any that seem unrelated to your kidneys or urinary function

All your medications and doses, including vitamins or other supplements that you take

What treatment approach do you recommend? What are my other treatment options?

What are the possible side effects of treatment?

Could my condition go away on its own?

I have other medical problems. How can I manage them together with this condition?

Is there anything I can do at home to help with my symptoms?

What can I expect in the long term?

If I need a kidney transplant, will that cure me or can the disease come back?

Do you have any printed materials I can take with me? What websites do you recommend?

Don't hesitate to ask other questions as they occur to you during your appointment.

What to expect from your doctor

Your doctor may ask you questions such as:

Have you noticed any symptoms?

When did you first begin experiencing symptoms and how long have they lasted?

Does anyone in your family have a kidney disease?

Do you have high blood pressure?

Do you have diabetes?

Does anything seem to improve your symptoms? Worsen your symptoms?

To diagnose membranous nephropathy, your doctor may start with a detailed medical history and a physical exam. Your doctor may also recommend certain tests to identify possible causes and to determine how well your kidneys are working. These tests might include:

Urine tests. You may be asked to provide a urine sample so that your doctor can determine the amount of protein present in your urine.

Blood tests. From a sample of your blood, your doctor can test your cholesterol and triglyceride levels to see if they're elevated. Your doctor may also check your kidney function with a creatinine blood test. Fasting blood sugar and glycosylated hemoglobin tests check for diabetes. Other blood tests may reveal autoimmune diseases or infection with viruses, such as hepatitis B or hepatitis C.

Antinuclear antibody (ANA) test. The ANA test checks a sample of your blood for the presence of antinuclear antibodies, substances which attack your body's own tissues. High levels of antinuclear antibodies indicate an autoimmune disease.

Imaging exam. An ultrasound or computerized tomography (CT) scan allows your doctor to see the structure of your kidneys and urinary tract.

Kidney biopsy. In this procedure, your doctor removes a small piece of your kidney to examine under a microscope and identify what type of kidney disease you have. Kidney biopsy can also assess how much kidney damage has occurred and evaluate the effectiveness of treatment.

In some cases, membranous nephropathy occurs without any noticeable symptoms, and your doctor may discover the condition when the results of a routine urine test (urinalysis) show elevated protein levels in your urine (proteinuria).

Treatment of membranous nephropathy focuses on addressing the cause of your disease and relieving your symptoms. There is no certain cure.

In cases where membranous nephropathy is caused by a medication or another disease — such as a cancerous tumor — stopping the medication or controlling the other disease usually improves the condition.

Low risk of advanced kidney disease

With membranous nephropathy, you're considered at low risk of developing advanced kidney disease in the next five years if:

Your urine protein level remains less than 4 grams a day for six months

Your blood creatinine level remains in the normal range for six months

If you're at low risk of advanced kidney disease, treatment of membranous nephropathy usually begins with conservative measures, including:

Decreasing swelling (edema) with water pills (diuretics), which help remove sodium and water from your blood

Controlling cholesterol levels with statin medications

Decreasing blood clot risk with an anticoagulant medication

Reducing the amount of salt in your diet

Up to 30 percent of people with membranous nephropathy have a complete resolution of symptoms (remission) after five years without any treatment, and 25 to 40 percent have a partial remission. Doctors generally prefer to avoid using strong drugs — and their potential side effects — early in the course of the disease, when there's a chance that the disease will improve on its own.

Moderate to high risk of advanced kidney disease

Your doctor may recommend more intensive treatment as the amount of protein in your urine increases. The greater the protein level, the greater the risk to your health:

Moderate risk. With membranous nephropathy, you're considered at moderate risk of advanced kidney disease if your urine protein level stays between 4 and 8 grams a day with a blood creatinine level at normal or near normal during six months of observation. About half the people with these signs develop serious kidney disease over five years.

High risk. With membranous nephropathy, you're considered at high risk of advanced kidney disease if your urine protein level is persistently greater than 8 grams a day for three months or if your kidney function is below normal or falls below normal during the observation period. About 3 in 4 people with these signs have a high risk of progressing to serious kidney disease over five years.

For those at moderate to high risk of developing advanced kidney disease, treatment of membranous nephropathy might include:

Medications to suppress your immune system. If your proteinuria is getting worse, your doctor may prescribe a combination of a corticosteroid medication with a chemotherapy drug to suppress your immune system. Alternatively, a type of drug called a calcineurin inhibitor might be given if you can't tolerate or choose not to take a chemotherapy drug.

These medications can effectively reduce urine protein levels and stop the progress toward kidney failure. But the medications have significant side effects, they don't help everyone, and symptoms return for many people after treatment ends. Some of the side effects of chemotherapy drugs — such as risk of bladder cancer, leukemia and infertility — may occur many years after taking the drug.

If you don't respond to a first course of immunosuppressive therapy, or you have a relapse, you may benefit from a second course of treatment.

Rituximab (Rituxan). Rituximab has shown effectiveness in people who haven't benefited from immunosuppressive therapy. The drug kills B cells in the immune system — the cells that produce antibodies that damage the glomeruli. However, use of this drug is still experimental and rituximab is expensive and not generally covered by insurance.

Talk to your doctor about how to reduce your chances of developing kidney disease. Your doctor may suggest that you:

Have regular checkups

Follow your prescribed treatment for diabetes or high blood pressure

Lose excess weight by following a healthy diet and regular exercise program

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